Heat treating apparatus



Aprii 8, 1941. R. P. KOEHRING HEAT TREATING APPARATUS Filed May 9, 1938 2 Sheets-Sheet l INVENTOR Remus P Koeflame ATTORNEYS April 1941- R. P. KOEHRING HEAT TREATING APPARATUS Filed May 9, 1938 2 Sheets-Sheet 2 m fim INVENTOR Romano P. Kosmzme Y k ATTORNEYS Patented Apr. 8, 1941 HEAT TREATING APPARATUS Roland P. Kochring, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a

corporation of Delaware Application May 9, 1938, Serial No. 206,727

2 Claims. (Cl. 266-5) This invention relates to heat treating furnaces and more particularly to furnaces in which the temperature is equalized due to a circulation of the gases therein as caused by the injection of gas at a high velocity,

An object of the invention is to provide a furnace which includes a bafile disposed between the charge to be heated and the heating element thus forming a restricted passage, means also being provided for injecting gas under high velocity into said furnace through said restricted passage, and thereby causing circulation of the atmosphere within the furnace.

A still further object of the invention is to provide an apparatus for equalizing the temperatures within the controlled atmosphere furnace which comprises, means for injecting controlled atmosphere gas into the furnace through a restricted passage adjacent the heating means and thereby causing circulation of the atmosphere Fig. 1 illustrates a longitudinal view of a con-- trolled atmosphere furnace which includes a cooling chamber.

Fig. 2 isa section taken on the line 2-2 of Fig. 1.

Fig. 3,is a fragmentary sectional view showing the relationship between the heating elements and injector jets as used in the furnace taken on line 33 of Fig. 2.

Fig. 4 is a fragmentary view taken on line l4 of Fig. 2, and,

Fig. 5 is a modified form of baffle construction.

In the usual type of controlled atmosphere furnace, the controlled atmosphere such as, hydrogen, nitrogen, carbon monoxide, carbon dioxide, etc. or mixtures thereof, is admitted into the heating chamber at a low velocity and under a pressure slightly in excess of atmospheric pressure. This pressure ratio prevents the ingress of any substantial quantity of atmospheric air and thereby maintains the controlled atmosphere within the furnace. In such controlled atmosphere furnaces, and in fact in any type of heat treating furnace, the charge to be heated is usually not heated to any degree of uniformity due to the poor circulation of atmosphere within the furnace. This is explained by the fact that the gases in the upper part of the furnace are usually hotter than the gases in the lower part thereof, and as a result the upper portion of the charge is usually heated to a higher temperature than the lower portion thereof. Similarly when a number of small charges are placed within the furnace those adjacent the radiating surfaces of the heating elements are heated at a higher rate and to a higher temperature than the charges which are shielded from the heating surfaces by the remainder of the charge. Furnaces of this character are used in the heat treating of metallic articles such as dies and other tools and are likewise used in sintering powdered metal briquettes and the like.

In an effort to overcome the aforementioned difiiculties, circulating fans have been utilized within heat treating furnaces to cause a circulation of the atmosphere therein, but as yet it has been found impractical to utilize such fans in furnaces wherein the temperature is in excess of 1600 F. In the sintering furnaces hereinbefore mentioned temperatures are normally maintained between l800 and. 2300" F., and therefore the use of circulating fans is impractical.

The present invention is particularly concerned with providing uniform temperatures throughout a heat treating furnace without the use of a fan and is preferably used in connection with controlled atmosphere furnaces wherein it is necessary to introduce a controlled atmosphere gas to replenish and maintain the atmosphere within the furnace.

Furnaces of the type described are heated in a number of manners, for example, by burning gaseous fuel on the outside of the muffle and thereby heating the walls thereof, or by the use of electric heating elements disposedalong the inner walls of the heating chamber, such a type of furnace being shown in the drawings for illustrative purposes only.

Referring to the drawings a controlled atmos phere furnace 20 is shown in Fig. 1 which includes a heating chamber 22 that connects through a tubular section 24 with a cooling chamber 26. A continuous type of conveyor belt 28, which passes over sprockets 30 and 32, is disposed within the heating chamber 22 and passed through cooling chamber 26. The entry to the heating chamber 22 is at 34, and the conveyor belt 28 passes through the entry 34 in a clockwise direction thereby conveying any material placed thereon first through the heating chamber 22 and then through the cooling chamber 26,

whence the material emerges from the furnace at 36. The belt 28 is driven by suitable means (not shown) and the rate of travel thereof may be controlled so that material placed thereon remains within the heating chamber a prede termined period.

Fig. 2 shows a section through the furnace illustrated in Fig. 1, and in this particular embodiment the furnace is heated by means of hichrome ribbon heating elements 40 disposed along the walls of the furnace. Similar elements may bedisposed on the top wall of the furnace as at M, if desired. A plurality of piers M are provided within the furnace to support a belt rack 46 which opens beneath the belt to provide free circulation of atmosphere therethrough. The belt 28 may be formed from a plurality of horizontally spaced bars 29 suitably hinged at their outer ends to a chain or other drivin between the battles 38 and the supporting frame 7 36 for the belt 28. Thus any downward fiow of the gas within the chamber must pass through the belt 28.

In order to create a circulation of air within the heating chamber, the controlled atmosphere gas is admitted to a feeder pipe 52 provided with a plurality of jets 54 therein. These jets inject the gas into the restricted passage between the bafile plates db and the wall of the furnace, and due to the high velocity with which the gas is injected and the restricted passage into which it is exhausted, an inspiration effect is created which entrains or draws the atmosphere within the furnace through the belt 28 and circulates it upwardly between the baiiles 60 and the walls of the chamber. It has been found that a very small quantity of controlled atmosphere gas is required for this purpose providing the velocity of the same at the jets is high. It is preferable to curve the upper ends of the bafiles d3 inwardly as at 56 so as to direct the fiow of atmosphere from the wall side of the baffie inwardly toward the center of the furnace. Thus, by supplying controlled atmosphere to the furnace under a velocity sumcient to cause an inspiration effect, a continuous circulation of the gas within the heating chamber is effected. Preferably the jets 5d are so placed as to be between the folds of the ribbon element also that the gas emitted therefrom does not impinge directly upon the heating element until the velocity thereof has been decreased. I

In the baffle type of design, as shown in Fig. 7, the bafiie it may be provided with longitudinal flange it at the wall side thereof to form a restriction in the passage. It has been found that such a design improves the atmosphere entrainment, but it should be understood that for most purposes such a design is not essential.

While the embodiment of the present inven-.

tion as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A continuous heat treating furnace comprising in combination, a furnace chamber, means for heating said chamber disposed adjacent the walls thereof, a continued conveyor support for the charge to be heated within the furnace for moving the charge through the furnace, said support comprising an open work structure for permitting free circulation of the furnace atmosphere therethrough, a baflie plate between said support and said heating means for forming a restricted passage with the wall of the furnace, said passage containing the heating means and having free ingress and egress to said chamber, and means for continuously introducing small quantities of controlled atmosphere gas under high velocity into said pas sage between said ballle and the wall of said chamber for causing the atmosphere within said chamber to be circulated due to the entrainment of the atmosphere within said furnace by the introduced gas, thereby causing the temperature within the chamber to be substantially equal throughout the chamber due to circulation thereof.

2. A continuous heat treating furnace comprising in combination, a heating chamber, means for heating said chamber and located adjacent a wall of said chamber, a support within the chamber for supporting and moving a furnace charge through the furnace, said support comprising an open work structure for permitting free circulation of the furnace atmosphere therethrough, a 1baflle between said support and said heating means for forming a restricted passage with the wall of the furnace, said passage containing the heating means and having free ingress and egress to said chamber, means cooperating with said baflle for substantially closing the space between the bafile and the adjacent edge of said support, and means for continuously introducing small quantities of high pressure controlled atmosphere gas into said passage for causing circulation of the furnace atmosphere due to entrainment thereof in said passage whereby the temperature of the furnage is maintained substantially equal throughou ROLAND P. KOEHRING. 

